In recent years the ability of enzymes to function as remarkably efficient chemical factories has been harnessed with considerable commercial success, in large part owing to increased technological competence in utilizing enzymes in immobilized enzyme systems. An immobilized enzyme system consists of a support matrix to which there is bound an enzyme. A support matrix is a structure characterized as having good physical integrity and favorable properties toward liquid flow under conditions experienced in fixed-bed reactors, and further characterized by having the ability to bind or immobilize enzymes with minimum perturbation of enzymatic action. By an immobilized enzyme system is meant the structure which results from immobilization of an enzyme on a support matrix.
An example of a support matrix and resulting immobilized enzyme system, and the one perhaps most closely related to the present invention, is that described in U.S. Pat. No. 4,141,857. The patentee's support matrix is a core support (porous inorganic oxide) impregnated with a polyamine subsequently cross-linked with an excess of a bifunctional reagent so as to provide excess pendant functional groups. One important characteristic of the prior art support matrix is that the polyamine is impregnated on porous material, with the polyamine in part deposited within the pores contributing to the surface of the support. Another important characteristic is that the polyamine is extensively cross-linked, including that part in the pores, thereby entrapping the material therein and firmly anchoring the resulting resin to the surface. The result is a resin, to which the enzyme is later bound, which is highly resistant to attrition, ablation, and other means of removal from the core support. It should be clear that there is a central role played by the pores of the support in giving rise to this latter property. Still another characteristic of this prior art is that the pendant functional groups become covalently bonded to enzymes, with the enzymes being firmly bound to the support matrix in the immobilized enzyme system. Such firm bonding is particularly useful when the inherent lifetime of the enzyme is long, that is, when physical removal would otherwise shorten the useful lifetime of the enzyme.
The advantages of the aforementioned prior art support matrix cannot be utilized in that class of enzymes whose inherent lifetime, as measured by its half-life under reaction conditions, is too short for such advantages to be experienced. Stated differently, a firm physical-chemical attachment of an enzyme and of the resin to a core support is irrelevant where the enzyme is deactivated faster than or competitively with the physical loss of enzyme and/or resin to which it is bound. The prior art support matrix advantages also cannot be fully utilized where its cost and the cost of immobilization is high relative to enzyme cost. That is, using a relatively inexpensive enzyme with a relatively expensive support matrix is not cost-effective. It is to these latter classes of enzymes that the present invention is particularly pertinent.
The invention here is a support matrix and immobilized enzyme system therefrom comprising a core support on the surface of which is deposited functionalized, water-insoluble polyethylenimine. In the support matrix of this invention the functionalized polyamine may be deposited on any surface; pores are unnecessary and superfluous not conferring any advantage. Another characteristic of this invention is that the functionalized polyamine is not cross-linked. Still another property is that the enzyme is bound by ion exchange forces, which are much weaker than the covalent bond of the prior discussed material. All these characteristics stand in bold contrast to the prior art.
The characteristics and differences alluded to in the preceding paragraph confer several distinct advantages to the support matrix of the present invention. One advantage is the simplicity of the composition and its preparation, both of which lead to substantial reduction in cost and time of preparation. Another advantage is that the support matrices are surface independent. That is, the support matrix and immobilized enzyme system may be prepared from a virtually unlimited number and nature of core supports in a variety of forms and shapes. Still another advantage is that the support matrix can be prepared with a uniform thickness of organic material serving as the enzyme binding material. Yet another important advantage of the materials of this invention is that after activity of the immobilized enzyme is reduced to the point of inutility the deactivated enzyme and the underlying binding material can be readily stripped or removed and the core support can be reused, thereby affording facile regeneration of the immobilized enzyme system. It is to be stressed that all these advantages confer maximum benefits when deactivation of the enzyme is at least competitive with physical loss of the enzyme from the immobilized enzyme system, or when the enzyme is relatively inexpensive, as elaborated upon above.